This invention relates to an incandescent multi-filament light bulb and more particularly to a multi-filament electric light bulb which is lightable one filament at a time.
Incandescent light bulbs are commonly used in most households and in many commercial establishments. However, it is well known that such bulbs have a limited life time and after a certain number of hours of operation, the bulbs will fail. In most cases of failure, an essential structural component, the light emitting filament burns out rendering the light bulb inoperative. At times, a burned-out light bulb creates a safety hazard, as for example, when the bulb had been used to illuminate a stairway or other obstacle. At other times, the loss of a light bulb is an inconvenience which may be exacerbated by a failure to stock a reserve bulb.
There have been numerous efforts to overcome the short comings of single filament bulbs. For example, a U.S. Patent of Dill, U.S. Pat. No. 3,886,400 discloses a multi-filament light bulb wherein the filament can be individually energized by movement of a selector mounted on the base of the bulb. As disclosed therein, the selector is moved circumferentially to energize a different filament so that the bulb does not have to be thrown away when a first filament fails.
A rotatable multiple filament lamp and socket adapter is disclosed in the U.S. Pat. No. 4,121,134. As disclosed therein, a multi-filament lamp has one set of ends of all filaments connected to a common conductor and the ends of another set individually connected to separate conductors. The filaments are sequentially lightable by turning the lamp in a socket adapter that is screwed into a standard light socket.
A further approach to a multiple filament incandescent bulb is disclosed in a U.S. Pat. No. 4,179,637 of Santora. The Santora patent discloses a bulb with a plurality of filaments, the first of which is mounted between a first and second current supply member to emit light in response to a flow of electrical energy. The remainder of the filaments on reserve or reserve filaments are mounted between the first and second current supply members with electrical connection being established only between the first current supply member and the reserve filament. Biasing means are provided for urging the second current supply member in the direction of a longitudinal axis defined by the filaments. The biasing force is counteracted by the first filament and in later stages of the life of the bulb by one of the reserve filaments.
Notwithstanding an apparent lack of commercial success of the aforementioned multi-filament bulbs, it is presently believed that there may be a relatively large commercial demand for an improved multi-filament bulb in accordance with the present invention. It is believed that there will be a demand because the multi-filament bulbs in accordance with the present invention have a number of advantages over the prior art bulbs. For example, the multi-filament bulbs disclosed herein will have a longer life than a single filament bulb. The bulbs will also provide a built-in back-up for bulb failure without a need for a special socket or attachment. Further, the multi-filament bulb with one embodiment of the invention may be readily inserted in a bayonet type of bulb.
It is also believed that the multi-filament bulbs in accordance with the present invention can be manufactured and sold at a competitive price with a considerable savings in raw material since one multi-filament bulb will replace three or four single filament bulbs. A further advantage is that the bulbs, in accordance with the present invention, provide advance notice to a consumer or householder when it is time to order or inventory a replacement bulb, as for example, when the householder selects the last filament.
In addition, the multi-filament bulb in accordance with the present invention may be readily changed from one filament to the next by removing the bulb from the socket, making the change and reinserting the bulb in the socket. Further by removing the bulb from the socket, there is no danger of an electric shock. Also, by manually changing from one filament to the next, it is apparent how many filaments are left which alerts a householder to order a replacement when the last or next-to-last filament is selected.
In essence, the present invention contemplates an incandescent multi-filament electric light bulb which is lightable one filament at a time. The multi-filament electric light bulb includes a sealed glass envelope and a base fixed to the glass envelope in the same manner as a conventional electric light bulb. The incandescent light bulb, in accordance with the present invention, includes a plurality of incandescent filaments and means including a glass stem or support for supporting the filaments within the glass envelope. A fist and second electrical contact which are electrically isolated from one another are disposed in the base of the bulb. These two contacts may also be provided in a conventional manner with one of the contacts in the center of the bottom of the base and the other as a metal ring extending around the base for contact with a metal ring in a socket. The multi-filament bulb also includes a common connector for connecting each of the filaments to one of the electrical contacts and in a preferred embodiment of the invention to the electrical contact which is in the center bottom portion of the base. Switch means are also disposed in the base for completing an electrical circuit which includes the first and second contacts, the common connector and one of the filaments to energize the filament and illuminate the bulb, when the bulb is inserted in a suitable socket and connected to a source of electrical energy. A key element of the present invention resides in the switch means which includes a ring-shaped insulater, preferably glass, which is positioned within the base and which has a plurality of electrical contacts thereon. The contacts on the ring-shaped insulator are electrically isolated from one another and each of the contacts on the ring-shaped insulator are electrically connected to one of the filaments. The multi-filament light bulb also includes a plurality of inwardly depressable switches or metal tabs with each inwardly depressable switch adjacent to one of the contacts on the ring-shaped insulator. Thus, when a filament burns out, the bulb can be removed from the socket and one of the switches depressed radially to connect another of the filaments to the first and second contact to complete the circuit. Then when the bulb is re-inserted in a socket and connected to a source of electricity, it is illuminated.
The invention will now be described in connection with the accompanying drawings wherein like reference numerals have been used to indicate light parts.